MBB 222 Study Guide - Final Guide: Pyrimidine Dimer, Dna Glycosylase, Ap Endonuclease
Document Summary
The remaining nick is sealed by dna ligase. Enzyme that recognizes dna lesions and removes the affected base by cleaving the n-glycosyl bond. Each dna glycosylase is specific for one type of lesion. Ex. ) for cytosine deamination (forming uracil), base-excision repair is done using uracil dna glycosylase. Ap site (abasic site): the apurinic/apyrimidinic site in dna created by cleavage from dna glycosylase. Ap endonuclease: enzymes that cut the dna strand containing the ap site. This repair is used for dna lesions that cause large distortions in the helical structure of dna. A multisubunit enzyme hydrolyzes the phosphodiester bonds on either side of the distortion. The excised nucleotides are released from the duplex with the help of a helicase. The gap is filled in by dna pol i and the nick is ligated with dna ligase. Mbb222 exam vocab definitions: base/nucleotide-excision and pyrimidine dimer. When the offending base is removed and replaced.